Stridulation Frequency Dependence on Music Genre in Acheta domesticus (Linnaeus)(Orthoptera: Gryllidae)

Michael Boachie-Mensah

Edited by J. Michelle Shannon

Abstract: Crickets are mainly nocturnal species known for the loud, persistent, chirping sounds many of their species make. Cricket chirping, or stridulation, is produced when the insect rubs together stridulatory organs located on the forewings. Stridulation is a form of intraspecific acoustic communication used by males to entice females. However, predators and parasitic insects may exploit their singing, using it to find their cricket prey. Consequently, crickets cease chirping when they sense sound frequency vibrations nearby, indicating that a predator is nearby. In this experiment, the cricket species Acheta domesticus (Linnaeus)(Orthoptera:Gryllidae) was used to test stridulation frequency differences based on exposure to different music genres. Crickets were exposed to either silence (control), hip hop, jazz, country, or classical music. During this music exposure period, the number of chirps was counted for one minute. Stridulation frequency was 83.3 chirps per minute for the control setting, 65 chirps per minute for classical music, 61.3 chirps per minute for country music, 54 chirps per minute for jazz music, and 41 chirps per minute for hip hop music. Causative factors for this trend may be due to neurological characteristics of the cricket. A major auditory sensory neuron, Ascending Neuron 1 (AN1), is excited by both high- frequency sounds and self-generated chirps. We conclude that music genres dominated by high- frequency sounds, such as hip hop and jazz, stimulate AN1, causing increased auditory information to be sent to the brain, leading to decreased stridulation as crickets interpret this information as the presence of a possible threat.

Keywords: Acheta domesticus, stridulation, music genre, vibration frequency

Crickets are nocturnal insects of the order the forewings. There are two specialized Orthoptera and the family Gryllidae. They body parts on the tegmena: a scraper are one of the most common stridulatory (plectrum) on one tegmen and a file on the species. Stridulation refers to the other (Fig.1). Both the scraper and the file phenomenon of sound production by the have sclerotized ridges that are chisel-like rubbing together of body parts. Other larger and resemble teeth). Sound is produced when animals, such as fish, snakes, and spiders also the forewings move back and forth and the stridulate. At any given time during the night, teeth of both the scraper and the file rub crickets can be heard outside making loud against each other (Fig.2). This causes the chirping noises. In crickets, the stridulatory forewings to vibrate as fast as the teeth, organs are found on the tegmena, which are producing pulses with a whistle-like tone (Stephen and Hartley 1995).

Figure 1. The stridulatory files of the cricket species (A) Isophya nagyi, (B) Isophya camptoxypha, (C) Isophya ciucasi, (D) Isophya posthumoidalis, and (E) Isophya sicula. Figure 2. The scraper is on the right wing and the file on the (H) Close detail of the stridulatory file of Isophya nagyi left wing. The bottom figure shows the wings moving back (Szövényi et al. 2012). and forth, causing the file to strike the scraper. This generates the chirp we hear from crickets ("Crickets (Insects)" 2017). Generally, only male crickets stridulate since Environmental temperature also plays a most female crickets do not have the significant role in the frequency of chirping necessary adaptations to stridulate (Chapman due to the cold-blooded nature of crickets 2013). The purpose of such behavior is to (Dolbear 1897). For example, as temperature attract females and repel other males. Once rises, chirping occurs more rapidly. The successful mating has occurred, a triumphal present research was conducted to determine song is produced that serves to encourage the the effect, if any, that different music genres female cricket to lay eggs instead of have on cricket stridulation. searching for a new mate (Chapman 2013). Although crickets do not have ears, they can

indeed hear. Hearing is achieved when a pair Morphological aspects of the tegmena, as of tympanal organs located on their legs well as environmental factors, direct both the vibrates in response to vibrating air particles, length and frequency of cricket chirping or sound (Schmidt et al. 2011). Once these (Huber 1962). For example, the number of tympanal organs vibrate, a receptor known as teeth that are rubbed against each other the chordotonal organ translates the vibration during each strike determines the length of into a nerve impulse that is sent to the brain the chirp. for processing (Christensen 2005).

Each music genre has a distinct sound, Lastly, we played compositions by enabling genre categorization to be possible. Beethoven for the classical music trial. We thus hypothesized that due to the varying During each trial, while the music was vibration patterns of different musical genres, playing, we counted the number of chirps the crickets would alter their stridulation crickets made during a one-minute time frequency. More specifically, we period. Successive trials were conducted and hypothesized that the more discordant chirp averages for each genre of music were vibrations of music genres like jazz and hip calculated. hop would decrease stridulation frequency. Results Materials and Methods Between the four musical genres tested, the We used adult Acheta domesticus crickets crickets had the highest frequency of chirping (house cricket) purchased from Petco Animal when classical music was played. They Supplies, Inc. (San Diego, CA). About 100 chirped at a rate of 65 chirps per minute when crickets were used in the experiment. classical music was played. Country music Different genres of music were played in the produced the second-highest number of vicinity of the crickets, loud enough for them chirps, with crickets chirping an average of to hear it. Four different musical genres were 61.3 chirps per minute. Jazz and hip hop tested: hip hop, jazz, country, and classical music produced the lowest number of chirps music. For the hip hop music trial, we played per minute: 54 and 41 chirps per minute, songs by Future. For the jazz music trial, respectively. All of these values were popular John Coltrane songs were played. significantly lower than the stridulation For the country music trial, we played songs frequency during silence, which was by country music artist Dierks Bentley. recorded to be 83.3 chirps per minute (Fig. 3).

Stridulation Frequency Dependence on Music Genre

100 90 80 70 60 50 40 83.3 30 61.3 65

Number of Chirps of Number 54 20 41 10 0 Control Hip Hop Jazz Country Classical Music Genre

Figure 3. Bar graph comparing the number of chirps per minute between crickets during silence and crickets exposed to hip hop, jazz, country, or classical music.

Discussion and Conclusion examining the cricket’s response to changes in musical genre. The objective of the present study was to compare the stridulation frequency of Viewing music through a spectrum analyzer crickets while different genres of music are produces astonishing results. Spectrum played. Crickets are always on the alert for analyzers measure acoustic pressure waves, predators so they are very sensitive to allowing the observation of changes in changes in vibration. Even subtle changes in frequency. Amazingly, analyzing a lot of movement, such as a human sneaking up on music that belongs to the same genre of music a cricket, can cause it to go silent. Such leads to the detection of patterns with respect sensitivity to vibrations inevitably means that to energy distribution over the frequency crickets respond to subtle changes in spectrum (Anderton 2015). Although vibration between genres of music. In fact, generalization across the different types of Dr. Natasa Stritih, a researcher at the music in a genre is faulty, it is useful to National Institute of Biology, made the examine recurring similarities. For example, following statement about vibrational the spectral response curve for classical sensitivity in the cricket; “With respect to music (Fig. 4) depicts a rapid roll-off in the sensitivity of the vibratory neurons in the treble range (high frequency, 2 kHz – 16 cave cricket, their acceleration response kHz). This roll-off may be due to the absence thresholds reached down to 0.0005 to 0.01 of thrashing cymbals or synths with lots of m/s2, making them among the most sensitive harmonics. In contrast, the spectral response vibrational responses ever detected in curve for the hip hop music genre show’s animals” (Stritih 2010). This sensitivity to significantly more midrange and bass vibrational changes is implied when emphasis (Fig. 5). The low-frequency increase is characteristic of the increased bass Sound is defined as the propagation of guitar/synth bass found in hip hop music. mechanical vibration waves of pressure and Also characteristic of hip hop is high-hat and displacement. The higher frequency the percussion parts, leading to the increase in sound, the more vibrations. As the higher high-frequency vibrations. frequency sound characteristic of hip hop and jazz reached the tympanal organs on the cricket, they reacted by increasing their frequency of stridulation. More vibrations in their surroundings could indicate the presence of a predator, so less chirping is ideal to not draw too much attention. In contrast, the low-frequency sounds in classical music produced less of an effect on stridulation frequency. Fewer vibrations in the environment meant the cricket was relatively safe and could continue chirping.

Figure 4. The spectral response curve for a typical song from Another plausible explanation for the the classical music genre. The rapid roll-off in the treble range is expected due to a lack of thrashing cymbals, synths, changes in stridulation frequency is seen in or boosted treble. Minimal processing also contributes to the neurobiology of the cricket. A pair of low high-end energy. ascending neurons known as Ascending Neuron 1 (AN1) receives excitatory input from receptor neurons in each tympanal organ and sends the input to the brain (Pollack 2014). AN1 is sharply tuned to sounds with a frequency pf 4.5 kHz, characteristic of the male calling song (Poulet and Hedwig 2002).

Such high-frequency sounds are commonly found in the hip hop music genre (Anderton 2015). Researchers at the University of Cambridge showed that AN1 is rhythmically excited during sonorous chirps, or two- Figure 5. The spectral response curve for the hip hop music winged stridulation (Poulet 2005). As the genre. There is significant midrange emphasis (vocals and instruments like guitar and piano), more bass, and a bit tegmina opened at the beginning of a chirp, a more high-frequency action. (Anderton 2015). depolarizing potential occurred in AN1. This excitation of AN1 in caused neuronal spikes,

indicative of brain activity. We propose that This somewhat extensive music review was a sort of feedback loop causes the results we provided to better understand our results. witnessed in the experiment. Cricket chirping and high-frequency music in the environment simultaneously excite AN1, causing an increase in auditory information being sent to the brain. Crickets then respond to increased auditory input by decreasing the number of chirps, an instinctual response to sound vibrations. This phenomenon does not occur with the lower frequency music because the threshold for responding to high frequencies in the cricket brain is much lower than the threshold for low frequencies (Brodfuehrer and Hoy 1990).

In conclusion, crickets exhibit stridulation frequency differences when exposed to different genres of music. This is due more to general differences in the balance between frequency components characteristic of the genres of hip hop, jazz, country, and classical music. Classical music had the smallest effect on stridulation frequency, while hip hop music decreased stridulation frequency significantly. In the future, we will examine the effect that specific frequencies have on stridulation. A broader range of music genres will also be evaluated on stridulation frequency effect.

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